Parallel mechanism

ABSTRACT

A carving apparatus including a spaced axially aligned tool and tracer and parallel mechanism including two spaced surfaces for carrying a workpiece and a pattern and for simultaneously presenting the pattern and workpiece to the tracer and tool, respectively. The parallel mechanism includes a base portion moveable on a reference surface and includes a mechanism for rendering the workpiece and pattern-carrying surfaces movable toward and away from the reference surface while continuously maintaining them parallel to each other and parallel to the reference surface. The parallel mechanism includes a generally boxlike structure including the pattern and workpiece carrying surfaces and identical and oppositely disposed endpieces connecting those two surfaces. At each end it includes a pair of identical and reversely disposed leg members, each pivotally connected to the boxlike structure at one end and having an opposite end operably engageable with the reference surface, and with means providing a pivotal connection between the two legs of each pair at a point intermediate the point at which they are pivoted to the boxlike structure and their opposite ends. The pivot point between the two legs of each pair is movable generally normal to the reference surface and is spring biased in one direction and movable against the spring in the opposite direction. An alternative embodiment includes selectively adjustable means for limiting the movement of the mechanism in a direction normal to the reference surface.

United States Patent Lenz [54] PARALLEL MECHANISM Primary ExaminerPaul R. Gilliam AttomeyDonald R. Sjostrom [57] ABSTRACT A carving apparatus including a spaced axially aligned tool and tracer and parallel mechanism including two spaced surfaces for carrying a workpiece and a pattern and for simultaneously presenting the pattern and workpiece to the tracer and tool, respectively. The parallel mechanism includes a base portion moveable on a reference surface and includes a mechanism for rendering the workpiece and pattern-carrying surfaces movable toward and away from the reference surface while continuously maintaining them parallel to each other and parallel to the reference surface. The parallel mechanism includes a generally boxlike structure including the pattern and workpiece carrying surfaces and identical and oppositely disposed endpieces connecting those two surfaces. At each end it includes a pair of identical and reversely disposed leg members, each pivotally connected to the boxlike structure at one end and having an opposite end operably engageable with the reference surface, and with means providing a pivotal connection between the two legs of each pair at a point intermediate the point at which they are pivoted to the boxlike structure and their opposite ends. The pivot point between the two legs of each pair is movable generally normal to the reference surface and is spring biased in one direction and movable against the spring in the opposite direction. An alternan've embodiment includes selectively adjustable means for limiting the movement of the mechanism in a direction normal to the reference surface.

16 Claims, 7 Drawing Figures PATENTEMB 8|972 3.640.231

sum 1 Q5 3 I NVEN'TOR.

BY f c/Of/ O. LEA/Z ATTOPA/EV PARALLEL mcrmmslvr BACKGROUND OF INVENTION Parallel mechanisms generally have been proposed in many forms and for many purposes. The applicant's US. Pat. No. 3,456,556 entitled Tracer Apparatus" and issued Aug. 7, 1969, discloses a carving device which uses a fixed, spaced, axially aligned, tracer and cutter or tool and a parallel mechanism with spaced pattern and workpiece carrying surfaces fixed in parallel relationship and with a mechanism for rendering these surfaces movable together both generally normal to and generally parallel to, the axes of the tool and tracer while continuously maintaining these surfaces normal to the axes of the tool and tracer. The beforesaid patent discloses one type of parallel mechanism which has been used in a device of this type. It is desirable that such a parallel mechanism be simple and relatively lightweight since it is intended primarily for home workshop use. In addition it should be attractive and have any moving parts enclosed as much as possible. It is essential that it be easily and economically producible so that it can be marketed at a relatively low and competitive price.

BRIEF SUMMARY OF INVENTION The present invention provides a parallel mechanism, especially adapted for use with a carver apparatus as described above, which is extremely simple and easy to produce. It utilizes a minimum number of different parts by, for example, using identical components on opposite ends and is especially adaptable for mass production so that it can be produced in large quantities and at relatively small costs. The moving parts are substantially all enclosed and the overall unit is attractive and streamlined in appearance. It provides for adjustment of the biasing force urging the parallel mechanism to one position and in an alternative embodiment provides means for selectively limiting the movement in the direction toward and away from the tracer and tool.

Specifically, the present apparatus includes a unique means for maintaining a movable member at a predetermined angle with respect to a reference surface while permitting movement of this member toward or away from the reference surface. It includes a pair of identical and reversely disposed leg members, each having the first end pivotally connected to the movable member and a remote end operably engageable with, and movable along, the reference surface. Intermediate the ends of these legs is the crossover point of the legs and at this point they are pivotally connected together by a pivot which is movable toward and away from the reference surface. A pair of these leg members is disposed at each end of the parallel mechanism which also includes spaced workpiece and pattern carrying members joined at their ends by identical and reversely disposed endpieces. These endpieces are formed with uniquely constructed bearing or pivot surfaces on which the leg members are mounted and maintained at different distances from the main surface of the end member so that the legs of a pair lie in two closely spaced-parallel planes. At the crossover point of each pair of legs they are pivotally connected by a movable member which is movable with respect to the end member and is preferably spring biased to urge the parallel mechanism to one position along a line extending toward and away from the reference surface. Identical and reversely disposed cover or housing members cooperate with the end plates and include abutment surfaces which maintain the leg members mounted on their pivot or bearing surfaces and which provide covers to enclose the major portions of the legs including the pivot points and the movable guide members. An adjustment screw is mounted in each of the housing members and engages the end of a spring which acts upon the guide member. The screw can be rotated to vary the tension on the spring.

This structure permits the use of a minimum number of different components and is extremely simple to assemble. It is readily adaptable for mass production so that it can be manufactured and marketed at a relatively low cost. An alternative embodiment provides means selectively movable to limit the range of movement of the parallel mechanism with respect to facilitate mass production.

Another object of the invention is to provide a parallel mechanism as described which is light in weight and easily operable in connection with a carrying apparatus or the like.

Another object of the invention is to provide a parallel mechanism of the type described which has spring-biasing means urging the parallel mechanism in one direction along a line extending toward and away from the reference surface and which includes means for adjusting the tension on the aforesaid spring means and thus the bias force exerted thereby'.

Still another object of the invention is to provide, in a parallel mechanism of the type described above, means for selectively limiting the range of movement of the parallel mechanism toward and away from the reference surface.

DESCRIPTION OF DRAWING FIG. 1 is a perspective view of a tracer or carving apparatus utilizingthe parallel mechanism of this invention.

FIG. 2 is an end view, with portions broken away, of the parallel mechanism of this invention.

FIG. 3 is a fragmentary cross-sectional view of the mechanism taken generally along line 3-3 in FIG. 1.

FIG. 4' is a cross-sectional view taken generally along line 4--4 in FIG. 3.

FIG. 5 is a horizontal cross-sectional view taken generally along line 55 in FIG. 2.

FIG. 6 is a fragmentary cross-sectional view, generally similar to that of FIG. 3, but disclosing an alternative fonn of the invention.

FIG. 7 is an end view, with portions broken away, disclosing the alternative embodiment of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION Referring first to FIG. 1, there is disclosed a tracer apparatus including a fixed stand portion 10 and a movable parallel mechanism 11. Stand portion 10 includes an upright or vertical leg member 12 which is attached by means (not shown) to a reference surface 13 which preferably is a horizontal surface and thus normal to leg 12. Extending from leg 12 and in spaced-parallel relationship with surface 13 is an arm 14, and extending parallel thereto and spaced thereabove is another arm 15. Mounted on the end of arm 14, above surface 13, is a tracer element 16 which has a vertical axis. Mounted on the end of arm 15 is a power-driven tool which may include a motor 17 driving a rotary tool 18 which also has a vertical axis and which is vertically aligned with tool 16 so that their axes coincide.

Parallel mechanism 11 includes a pair of longitudinally extending, generally flat members 20 and 21 connected by a pair of end members 22 and 23. Longitudinal members 20 and 21 are disposed in spaced-parallel relationship and are maintained in this position by the end members. Members 20 and 21 are preferably metal and may have mounted thereon further sheet or plate members 24 and 25, respectively. These members are preferably of a relatively soft material such as fiberboard and the like to protect the tool and tracer. Member 24 has mounted thereon a workpiece 26 while member 25 has a pattern 27 mounted thereon. Members and 21 are spaced at a distance substantially equal to the distance between the tips of tracer 16 and tool 18 and pattern 27 and workpiece 26 are substantially vertically aligned. Thus, pattern 27 is presented to tracer 16 and simultaneously workpiece 26 is presented to tool 18, and by moving the parallel mechanism 11 vertically and horizontally, pattern 27 is traced in workpiece 26. It will be appreciated that members 24 and may be secured to members 20 and 21 by appropriate means such as the screws which have been disclosed. The pattern and workpiece may be attached to these surfaces by any appropriate means but preferably by double-backed tape.

In the preferred form, longitudinal members 20 and 21 are identical and are extruded members formed with an inwardly extending L-shaped rib along each edge and with a plurality of generally T-shaped longitudinally extending ribs on the underside. This can best be seen in FIGS. 4 and 5. End members 22 and 23 are preferably identical and reversely disposed members. Member 22 can probably best be seen by referring to FIGS. 1, 2, 3, and 5. As seen there, the member includes a main surface which extends generally vertically in the device and at the upper end it extends to a width approximately equal to the width of member 20. There it has an inturned flange 22a extending normal to the main surface and which has a plurality of notches permitting the flange 22a to be press fitted into the end of member 20 with the notches accepting the legs of the T-shaped flanges thereon. The central portion of member 22 may be of reduced dimension but at its lower portion it again extends to approximately the same width as its upper portion and there it has an inwardly extending flange 22b which also is provided with a plurality of notches so that it can be press fitted into member 21 which, it will be recalled, is identical to member 20 and also has a plurality of longitudinally extending T-shaped ribs. Again, the notches accept the legs of the T-shaped ribs. Preferably longitudinal members 20 and 21 and the flanges 22a and 22b (and similarly identical flanges 23a and 23b on member 23) are formed so that they provide an interference fit and they are pressed together and normally require no other form of securing them together.

Members 22 and 23 are substantially symmetrical about vertical axes. The lower portions of these members, and for example reference will be made to member 22, have a pair of pivot or bearing surfaces thereon. The first of these surfaces is disposed on a slightly raised portion 32 which is spaced to the right (as seen in FIG. 2) of the vertical center of member 22. Raised portion 32 has an annular pivot or bearing surface 33. Symmetrically disposed on the opposite of the center axes is a raised portion 34 which is raised a substantially greater distance from the main surface of member 22, and which has an annular pivot or bearing surface 35. Mounted on end member 22 are a pair of substantially identical and reversely disposed leg members 36 and 37. Each of these members is generally flat and constructed of relatively rigid sheet metal or the like and is generally S-shaped. At one end each of these members is provided with a circular opening of sufficient diameter to accept the bearing surfaces on member 22. Leg member 36 is mounted on bearing surface 33 with a small lowfriction bushing member 40 disposed between the opening in leg 36 and the pivot surface. Similarly, leg 37 is mounted on pivot surface 35 and a thin generally tubular antifriction member 41 is disposed between pivot 35 and the opening in leg 37. Due to the fact that portion 34 is raised a substantial distance further from the main surface of member 22 than is portion 32, legs 36 and 37 lie in parallel, slightly spaced, planes. The opposite ends of these legs extend down and are adapted to operably engage, and be movable along, reference surface 13. These two legs, which together form a pair, cross over each other at a point intermediate their two ends. At this point they are pivotally connected together.

In the preferred embodiment this is accomplished by means of a guide member 40 which is preferably formed of a low-fricbest be seen by referring to FIGS. 2 and 3. As seen there, it includes an upper generally tubular portion with a central opening 41. At its lower end guide member 40 has a generally I- shaped cross section with a pair of spaced, horizontal, transversely extending flanges 42 and 43 connected by a vertically extending portion 44 of reduced thickness so as to provide a transversely extending opening 45 at the front of member 40 and a transversely extending opening 46 on the rear side of member 40. These two openings are substantially identical. At their crossover point, legs 36 and 37 have slightly enlarged arcuate portions generally symmetrical on opposite sides of the leg. This portion on the leg has been designated portion 37a in leg 37 and 36a in leg 36. Portions 36a and 37a provide rolling surfaces and together have a diameter approximately equal to the width of spaces 45 and 46 and the flanges 42 and 43 at the top and bottom of openings 45 and 46 provide cooperating surfaces on which these members roll. Thus, guide member 40 cooperates with the rolling surfaces provided by portions 36a and 37a to provide a pivot between legs 36 and 37. These legs are spaced by the upright portion 44 of member 40, and the pivot point between the two legs moves up and down, toward and away from the reference surface 13, as guide member 40 moves up and down. Preferably lower flange 43 has a rearwardly extending tab 43a which extends into a vertically extending slot 50 in end member 22 and limits the amount of vertical movement of guide member 40 with respect to end member 22, thus also limiting the vertical movement of the pivot point between legs 36 and 37.

Secured to end member 22 by appropriate means such as a plurality of screws 51, is a housing or cover member 52 having a main, generally vertically extending, surface which is disposed in spaced, generally parallel, relationship with the main surface of end member 22. As can best be seen in FIGS. 1 and 2, cover member 52 has a lower portion which is substantially equal in width to the lower porn'on of end 22 and of generally the same contour. At its upper end, member 22 thins into a relatively narrow upwardly extending neck portion. Member 52 is also symmetrical about a generally vertically extending center axis. The lower portion of member 52 has a generally circular, slightly extended, portion 53 to which is attached a relatively large knob 54, by appropriate means such as a screw 55 extending from the interior of member 52 into the knob. The neck portion 52a of housing includes a pair of spaced rib members 53 and 54 which provides guides to limit movement of guide member 40 in a transverse direction with respect to the device. The main surface of end member 22 and of cover member 52 provide guide surfaces to limit the movement of guide member 40 in the longitudinal direction with respect to the device. At its upper end, neck 52a has a slot 55 which accepts and holds an adjustment screw generally designated 56 having a head 57 and a collar 60 on opposite sides of a reduced-diameter neck portion 61. The neck portion 61 is disposed in slot 55 before cover member 52 is attached to end member 22 and once it is attached, it is entramped in the slot and the adjustment screw can be rotated but cannot be moved axially. Threaded onto adjustment screw 56 is a generally rectangular abutment member 62 which is disposed on the interior of neck 52a and is of sufficient dimension so that it cannot rotate therein. Thus, as adjustment screw 56 is rotated, abutment member 62 will be moved axially thereon. Abutment member 62 abuts the end of a coil spring 63, the other end of which extends into the tubular opening 41 in guide member 40 and abuts the bottom of opening 41. The biasing force exerted upon guide member 40, thus urging it downwardly on end member 22, is determined by the position of abutment member 62 on screw 56.

Cover member 52 has formed on the inside thereof (as best seen in FIG. 5) inwardly extending abutment members 70 and 71 aligned with bearing or pivot members 33 and 35, respectively, on member 22. Abutment surface 70 extends inwardly and generally concentric with the annular pivot member 33 and extends to a position substantially in engagement with, or tion material such as nylon, for example. This member can 75 just short of, the outer surface of leg 36, thus preventing movement of leg 36 outwardly so that it comes off from the pivot member 33. Diametrically opposed from abutment surface 70 and generally similar thereto is abutment surface 71 which extends inwardly a shorter distance than does abutment surface 70 because of the fact that leg 37 is disposed in a plane closer to cover member 52 than is leg 36. Abutment surface 71 extends substantially into engagement with, or just short of the outer surface of leg 37 and prevents it from moving outwardly off from pivot member 35.

It will be appreciated that end member 23 is identical to end member 22 and is simply reversed from it. A pair of legs 72 and 73 (leg 73 is hidden in all of the figures) are mounted on pivot surfaces 74 and 75, respectively, on member 23. A cover member 76, identical to cover member 52 is attached to end member 23 by appropriate screws or the like 77. Legs 37 and 72 are axially aligned as are legs 36 and 73. The remote ends of these legs, that is the ends which are adapted to operably engage the reference surface, are rigidly connected by appropriate means such as a tubular member 81) which is secured at its opposite ends to legs 37 and 72, respectively, by appropriate means such as screws 31. Thus, legs 37 and 72 are relatively rigidly connected together and move substantially as a unit as do legs 36 and 73. An appropriate knob, identical to knob 54, is secured to housing or cover 76.

The operation of the apparatus which has been described will perhaps be apparent. It is desired that members and 21, and thus workpiece 26 and pattern 27, be maintained parallel to reference surface 13 at all times while permitting movement of the parallel mechanism toward and away from the reference surface as well as parallel to the reference surface. Spring 63 acting upon guide member 40, and an identical spring inside of cover member 76 acting upon a guide member therein identical to guide member 40, urge the pivot points between the two pairs of legs downwardly, thus urging the parallel mechanism to the uppermost position permitted by the tab member 413a in a slot 50 and a corresponding tab and slot in member 23. The operator grasps the knobs and maneuvers the parallel mechanism so that tracer 16 follows the contour of pattern 27 and at the same time workpiece 26 is moved with respect to the rotary tool 18, thus causing the tool to carve in workpiece 26 a duplicate of the pattern.

As has been noted, many identical parts are utilized in this mechanism. Members 22 and 23 are identical as are cover members 52 and 76. All of the legs 36, 37, 72 and 73 are identical. Longitudinal members 2119 and 21 are identical. The guide members, the springs and the adjustment screw mechanisms in the two ends are identical. Thus, a minimum number of different parts is required for the mechanism and it can easily be assembled. Cover members 52 and 76 substantially enclose the moving parts of the mechanism thus keeping them clean and assuring that the operators clothing or hands do not become entangled in them. Also, they provide a neat appearance. It will also be noted that guide member 46 not only provides a pivot between legs 36 and 37 but, as indicated, is preferably formed of a material such as nylon and thus provides a low-friction pivot surface for them. The parallel mechanism thus operates very smoothly and easily and always maintains surfaces 20 and 21 parallel to the reference surface.

FIGS. 6 and 7 disclose an alternate form of the invention. in this form of the invention the generally circular extended portion 53 of cover member 52 has a circular opening concentric about the axis of knob 54. Rotatably mounted in this opening is an eccentric cam member 90. Guide member 4 9 has portion which provides a follower surface 91 cooperable with a cam surface 92 on cam member 96. Cam surface 92 engages the underside of the follower surface 91 and thus limits the downward movement of guide member 40 with respect to end plate 22. As was discussed previously, movement of guide member 40 downwardly with respect to end plate 22 causes upward movement of members 20 and 21. Cam surface 92 is contoured so that as knob 541 is rotated counterclockwise, the amount of movement permitted is lessened. This can best be seen in FIG. 7 where cam surface 92 is disclosed in dotted lines. Opposite from cam surface 92, cam member has a surface with a plurality of detend notches 93 which are cooperable with a detent projection 94 on cover member 52. The plurality of the detent notches 93 provide a number of predetermined angular positions of cam 90 with respect to housing member 52 and, once the projection 94 is extended into one of these notches, it provides a relatively fixed setting of the cam 90. Preferably cam member 90 is fomred of a plastic material and is flexible enough so that it will flex and allow the cam to be rotated, separating projection 94 and notch 93, but this takes considerable force and in normal operation of the device the cam will remain stationary.

This alternate feature may be desirable in some instances so that the degree of movement of the parallel mechanism can be limited when work is initially done upon a workpiece. if an inexperienced operator were to rapidly move the workpiece into engagement with the rotating tool 18, he might damage the tool or, more likely, might tend to chip the workpiece. Thus, an operator may set the cam 90 so as to permit only very limited movement of the parallel mechanism when he begins to carve the workpiece, and, as the workpiece is gradually carved to the shape of the pattern, he may gradually increase the amount of movement permitted.

It will be noted that this alternate arrangement utilizes all of the elements of the preferred embodiment previously described with the slight modification of cover member 52 and the addition of cam 90. All of the advantages described before as provided by the unique construction of the parallel mechanism are retained. It will be appreciated that a similar cam mechanism is utilized in housing 76.

Theinvention, and its features and advantages have been described in connection with the disclosure and description of a preferred embodiment and one alternate construction providing an additional feature. It will be appreciated that various modifications and alterations may be made without departing from the spirit of the invention.

The embodiments of the invention in which an exclusive property or right is claimed are defined as follows:

1. Apparatus for maintaining a first movable member at a predetermined angle with respect to a reference surface when moved toward and away from the reference surface, the apparatus comprising, in combination with said first movable member: a pair of substantially identical legs arranged in reversed relationship and crossing over each other, each of said legs having a first end portion operably engageable with and movable along the reference surface, each of said legs also having a second end portion; means pivotally connecting the second end portions of said legs to said first member; guide means movable with respect to the first member, said guide means having a portion pivotally carrying said legs providing a pivotal connection between said legs and defining a crossover position thereof at a point between said first and second end portions of said legs; and means secured to said first member cooperating with said guide means to limit movement of the guide means in a generally linear direction.

2. The apparatus of claim 1 including spring means acting upon the guide means providing a pivotal connection between said legs, said spring means urging said pivotal connection in a direction generally normal to the reference surface.

3. The apparatus of claim 1 wherein: the portion of said guide means has spaced guide surfaces; each of said legs has a third portion disposed on said guide surfaces, said third portion being intermediate the first and second end portions, said third portions having means providing a pair of oppositely disposed rolling surfaces together having a dimension substantially equal to the surface between said guide surfaces on said guide member; and said legs are disposed in generally parallel, closely spaced relationship, each with its rolling surfaces disposed between said spaced guide surfaces on said guide member, said rolling surfaces and said guide surfaces together providing a pivot for said legs.

4. Apparatus for maintaining a first movable member at a predetermined angle with respect to a reference surface when moved toward and away from the reference surface, the apparatus comprising, in combination: a first movable member having a generally rectangular frame and means providing a pair of spaced, generally parallel work surfaces, and spaced generally parallel end members connecting said work surfaces; a pair of legs disposed adjacent each of said end members, each pair of leg arranged in reverse relationship and crossing over each other, each of said legs having a first end portion operably engageable with and movable along the reference surface and a second end portion, means pivotally connecting the second end portion to the end member adjacent thereto, guide means providing a pivotal connection between said pairs of leg and defining a crossover position thereof at a point between said first and second end portions of said leg, a pair of substantially identical housing members, one cooperable with each of the end members to provide an enclosure at each end of the device; said guide means at each end of said device being disposed within said enclosures and movable therein generally normal to said work surfaces; said guide means providing the pivotal connection between said legs whereby the pivot therebetween is movable generally normal to said work surfaces.

5. The apparatus of claim 4 including means cooperable between said guide means and said end members and limiting the relative movement between said guide means and the adjacent end member.

6. The apparatus of claim 4 further including spring means disposed within each of said enclosures and acting upon the guide means therein to urge the guide means, and thereby the pivot between the legs of each pair, in a given direction.

7. The apparatus of claim 4 wherein: said end members are substantially identical and are disposed in spaced, generally parallel, reversed relationship and are connected by a pair of spaced, generally parallel, substantially identical, members providing the work surfaces; each of said end members and its cooperating housing member includes means providing the pivotal connection between the second end portions of said legs and said first member; the structure providing two substantially identical end structures connected by said work surfaces, said end structures being disposed in generally aligned and reversed relationship; means connecting the first end portions of the aligned ones of said leg at opposition ends of the device whereby the first end portion of the first one of the leg at a first end of the device is relatively rigidly connected to, and moves with, the first end of the aligned leg at the opposite end of the device, and the first end of the second leg at said first end of the device is relatively rigidly connected to, and moves with, the first end of the aligned leg at the opposite end of the device.

8. The apparatus of claim 6 further including means operably connected to said spring means and manually movable to selectively vary the tension on said spring and thereby the force urging said pivot point between said legs in its given direction.

9. The apparatus of claim 4 further including motion-limiting means cooperable with the means providing a pivot point between the legs of a given pair and in adjustable abutting relationship therewith to limit the movement of said pivot point in a given direction; and means for manually operating said limiting means to select the limit of movement of said pivot point.

10. Paralleling apparatus comprising: movable means including a generally boxlike structure including a pair of spaced, generally parallel, longitudinal members having a pair of work surfaces thereon and a pair of spaced, generally parallel, end members connecting opposite ends of said longitudinal members, said end members comprising two substantially identical members each having a main portion and being generally symmetrical about a line which is generally normal to said longitudinal members, each of said members having offset to one side of said centerline a portion providing an annular bearing member extending a first predetennined distance from the main portion and a second, symmetrically disposed, annular portion extending a second predetermined distance, greater than the first, from said main portion and providing a second bearing member spaced further therefrom than said first bearing member; two pairs of generally flat leg members, one of said pairs disposed at each end of the device, each of the leg members having an opening for accepting one of said annular bearing members, one of the leg members of each pair being pivotally mounted on the first bearing member and the second of the leg members of said pair being mounted on the second of said bearing members, whereby said leg members of each pair are disposed in relatively closely spaced, generally parallel positions, said leg members having opposite ends extending from the pivot points and operably engageable with a reference surface; a pair of housing members, one cooperable with each of said end members to enclose at least a portion of the leg members connected thereto; means connecting said housing members to said end members; and said housing members including abutment means cooperable with said leg members to maintain said leg members mounted on their respective bearing members.

11. The apparatus of claim 10 further including means operably connecting and providing a pivotal connection between the two leg members of each pair at a point intermediate their pivot points on said end member and the opposite ends of said leg members, the means providing this pivotal connection being movable with respect to the adjacent end member in a direction generally normal to the longitudinal members.

12. The apparatus of claim 1 1 wherein the means providing a pivotal connection between the two leg members of a given pair comprises a guide member disposed within the housing member, intermediate said housing member and the adjacent end member, said guide member being movable with respect to said end member and housing member in a direction generally normal to the work surfaces provided by said longitudinal members; and the apparatus includes means limiting the movement of said guide members with respect to said end members and housing members in said direction.

13. The apparatus of claim 12 further including means disposed within said housing member and acting upon said guide member and resiliently urging said guide member in a given direction along its line of movement; and means cooperable with said resilient means and manually operable to selectively vary the force exerted by said resilient means on said guide member.

14. The apparatus of claim 11 further including means generally parallel to said longitudinal members and connecting the aligned opposite ends of said leg members at opposite ends of the device whereby aligned opposite leg of the device are substantially rigidly connected and the opposite aligned legs move substantially as a unit.

15. The apparatus of claim 12 further including eccentric cam means disposed within each of the housing members and in abutting relationship with said guide means to limit the movement of said guide means with respect to said housing and end members; and means rotatably mounting said eccentric cam means whereby said cam means may be selectively angularly positioned to determine the limits of movement of said guide members; and detent means coacting between said cam means and the adjacent housing member to define predetermined angular positions of said cam means.

16. The apparatus of claim 10 wherein said housing members are substantially identical and each includes a main surface spaced from the main portion of the adjacent end member; and said abutment means includes a pair of extending abutment portions on each of said housing members and aligned with the extending bearing members of the cooperating end member, the abutment portion extending toward the shorter of said bearing members being longer than the abutment portion extending toward the longer of said bearing members whereby said abutment portions extend substantially to the surface of the leg members mounted upon the respective bearing members and maintain the leg members mounted on their respective bearing members. 

1. Apparatus for maintaining a first movable member at a predetermined angle with respect to a reference surface when moved toward and away from the reference surface, the apparatus comprising, in combination with said first movable member: a pair of substantially identical legs arranged in reversed relationship and crossing over each other, each of said legs having a first end portion operably engageable with and movable along the reference surface, each of said legs also having a second end portion; means pivotally connecting the second end portions of said legs to said first member; guide means movable with respect to the first member, said guide means having a portion pivotally carrying said legs providing a pivotal connection between said legs and defining a crossover position thereof at a point between said first and second end portions of said legs; and means secured to said first member cooperating with said guide means to limit movement of the guide means in a generally linear direction.
 2. The apparatus of claim 1 including spring means acting upon the guide means providing a pivotal connection between said legs, said spring means urging said pivotal connection in a direction generally normal to the reference surface.
 3. The apparatus of claim 1 wherein: the portion of said guide means has spaced guide surfaces; each of said legs has a third portion disposed on said guide surfaces, said third portion being intermediate the first and second end portions, said third portions having means providing a pair of oppositely disposed rolling surfaces together having a dimension substantially equal to the surface between said guide surfaces on said guide member; and said legs are disposed in generally parallel, closely spaced relationship, each with its rolling surfaces disposed between said spaced guide surfaces on said guide member, said rolling surfaces and said guide surfaces together providing a pivot for said legs.
 4. Apparatus for maintaining a first movable member at a predetermined angle with respect to a reference surface when moved toward and away from the reference surface, the apparatus comprising, in combination: a first movable member having a generally rectangular frame and means providing a pair of spaced, generally parallel work surfaces, and spaced generally parallel end members connecting said work surfaces; a pair of legs disposed adjacent each of said end members, each pair of legs arranged in reverse relationship and crossing over each other, each of said legs having a first end portion operably engageable with and movable along the reference surface and a second end portion, means pivotally connecting the second end portion to the end member adjacent thereto, guide means providing a pivotal connection between said pairs of legs and defining a crossover poSition thereof at a point between said first and second end portions of said legs, a pair of substantially identical housing members, one cooperable with each of the end members to provide an enclosure at each end of the device; said guide means at each end of said device being disposed within said enclosures and movable therein generally normal to said work surfaces; said guide means providing the pivotal connection between said legs whereby the pivot therebetween is movable generally normal to said work surfaces.
 5. The apparatus of claim 4 including means cooperable between said guide means and said end members and limiting the relative movement between said guide means and the adjacent end member.
 6. The apparatus of claim 4 further including spring means disposed within each of said enclosures and acting upon the guide means therein to urge the guide means, and thereby the pivot between the legs of each pair, in a given direction.
 7. The apparatus of claim 4 wherein: said end members are substantially identical and are disposed in spaced, generally parallel, reversed relationship and are connected by a pair of spaced, generally parallel, substantially identical, members providing the work surfaces; each of said end members and its cooperating housing member includes means providing the pivotal connection between the second end portions of said legs and said first member; the structure providing two substantially identical end structures connected by said work surfaces, said end structures being disposed in generally aligned and reversed relationship; means connecting the first end portions of the aligned ones of said legs at opposition ends of the device whereby the first end portion of the first one of the legs at a first end of the device is relatively rigidly connected to, and moves with, the first end of the aligned leg at the opposite end of the device, and the first end of the second leg at said first end of the device is relatively rigidly connected to, and moves with, the first end of the aligned leg at the opposite end of the device.
 8. The apparatus of claim 6 further including means operably connected to said spring means and manually movable to selectively vary the tension on said spring and thereby the force urging said pivot point between said legs in its given direction.
 9. The apparatus of claim 4 further including motion-limiting means cooperable with the means providing a pivot point between the legs of a given pair and in adjustable abutting relationship therewith to limit the movement of said pivot point in a given direction; and means for manually operating said limiting means to select the limit of movement of said pivot point.
 10. Paralleling apparatus comprising: movable means including a generally boxlike structure including a pair of spaced, generally parallel, longitudinal members having a pair of work surfaces thereon and a pair of spaced, generally parallel, end members connecting opposite ends of said longitudinal members, said end members comprising two substantially identical members each having a main portion and being generally symmetrical about a line which is generally normal to said longitudinal members, each of said members having offset to one side of said centerline a portion providing an annular bearing member extending a first predetermined distance from the main portion and a second, symmetrically disposed, annular portion extending a second predetermined distance, greater than the first, from said main portion and providing a second bearing member spaced further therefrom than said first bearing member; two pairs of generally flat leg members, one of said pairs disposed at each end of the device, each of the leg members having an opening for accepting one of said annular bearing members, one of the leg members of each pair being pivotally mounted on the first bearing member and the second of the leg members of said pair being mounted on the second of said bearing members, whereby said leg members of each pair are disposed in relatively closely spaced, generally parallel positions, said leg members having opposite ends extending from the pivot points and operably engageable with a reference surface; a pair of housing members, one cooperable with each of said end members to enclose at least a portion of the leg members connected thereto; means connecting said housing members to said end members; and said housing members including abutment means cooperable with said leg members to maintain said leg members mounted on their respective bearing members.
 11. The apparatus of claim 10 further including means operably connecting and providing a pivotal connection between the two leg members of each pair at a point intermediate their pivot points on said end member and the opposite ends of said leg members, the means providing this pivotal connection being movable with respect to the adjacent end member in a direction generally normal to the longitudinal members.
 12. The apparatus of claim 11 wherein the means providing a pivotal connection between the two leg members of a given pair comprises a guide member disposed within the housing member, intermediate said housing member and the adjacent end member, said guide member being movable with respect to said end member and housing member in a direction generally normal to the work surfaces provided by said longitudinal members; and the apparatus includes means limiting the movement of said guide members with respect to said end members and housing members in said direction.
 13. The apparatus of claim 12 further including means disposed within said housing member and acting upon said guide member and resiliently urging said guide member in a given direction along its line of movement; and means cooperable with said resilient means and manually operable to selectively vary the force exerted by said resilient means on said guide member.
 14. The apparatus of claim 11 further including means generally parallel to said longitudinal members and connecting the aligned opposite ends of said leg members at opposite ends of the device whereby aligned opposite legs of the device are substantially rigidly connected and the opposite aligned legs move substantially as a unit.
 15. The apparatus of claim 12 further including eccentric cam means disposed within each of the housing members and in abutting relationship with said guide means to limit the movement of said guide means with respect to said housing and end members; and means rotatably mounting said eccentric cam means whereby said cam means may be selectively angularly positioned to determine the limits of movement of said guide members; and detent means coacting between said cam means and the adjacent housing member to define predetermined angular positions of said cam means.
 16. The apparatus of claim 10 wherein said housing members are substantially identical and each includes a main surface spaced from the main portion of the adjacent end member; and said abutment means includes a pair of extending abutment portions on each of said housing members and aligned with the extending bearing members of the cooperating end member, the abutment portion extending toward the shorter of said bearing members being longer than the abutment portion extending toward the longer of said bearing members whereby said abutment portions extend substantially to the surface of the leg members mounted upon the respective bearing members and maintain the leg members mounted on their respective bearing members. 